In American English, double quotes are used normally (the "primary" style). If quote marks are used inside another pair of quote marks, then single quotes are used as the 'secondary' style.
Then, of course, there are the people who pepper their writing with speech marks/inverted commas at random intervals, sometimes with unforeseen consequences.
Somewhere there's a site with photos of such unfortunate examples of over-punctuation.
The one that stuck in my mind ( I'm sorry to say) was from a bake sale somewhere in the US. It showed a plastic bag containing some lumps of brown sludgy stuff, labelled:
"Fudge".
The punctuation says it all. Needless to say, the unappetising confectionery failed to sell.
now he is back, newly inspired.
Please, don't argue about single or double quotation marks. They don't make a world, and everyone will understand the intended meaning if he/she is willing. This is said by an OVERCORRECT/ "overcorrect"/ 'overcorrect' German teacher. Rules are the one thing, communication the other. Better this manageable disaster than the SMS-ruled usage of abbreviations. Of course, in cases of formal writing you have to follow the rules, no doubt.
The Blue Book's site:
"<em>Rule 8a.</em>
Quotation marks are often used with technical terms, terms used in an
unusual way, or other expressions that vary from standard usage.
<em>Examples:
It's an oil-extraction method known as "fracking."
He did some "experimenting" in his college days.
I had a visit from my "friend" the tax man.</em>
<em>Rule 8b.</em> Never use single quotation marks in sentences like the previous three.
<em>Incorrect: I had a visit from my 'friend' the tax man.</em>
The single quotation marks in the above sentence are intended to send a message to the reader that <em>friend</em> is being used in a special way: in this case, sarcastically. Avoid this invalid usage. Single quotation marks are valid only within a quotation, as per Rule 7, above."
It refers to single quote marks used as 'scare quotes' in American usage. 'Single' and American.
